CN101141919A

CN101141919A - Ultrasonic monitor for measuring blood flow and pulse rates

Info

Publication number: CN101141919A
Application number: CNA2005800433810A
Authority: CN
Inventors: 托马斯·英清·罗; 张龙永
Original assignee: Salutron Inc
Current assignee: Salutron Inc
Priority date: 2004-11-17
Filing date: 2005-11-15
Publication date: 2008-03-12
Also published as: WO2006055666A9; US20060106310A1; WO2006055666A1; EP1824389A1; EP1824389A4; US7798970B2; CA2587905A1

Abstract

An ultrasonic monitor implemented on a PCB includes a gel pad comprised of a gel layer and a membrane layer. Ultrasonic signals are transmitted between the ultrasonic monitor and a living subject through the gel pad. An air gap is formed in the PCB underneath transducer elements to provide for more efficient signal transmission. These features provide for a low power, low cost, more efficient ultrasonic monitor. The entire ultrasonic monitor may be encapsulated in plastic, a gel, or both to provide water resistant properties.

Description

Ultrasonic monitor for measuring blood flow and pulse rate

Cross reference to related invention

This non-provisional application relates to the following patent applications:

U.S. patent application Ser. No. 10/346,296, filed on.1/15/2003;

U.S. patent application Ser. No. 10/758,608, filed on 7/14/2004, which is a continuation-in-part application of parent non-provisional patent application Ser. No. 10/346,296, filed on 15/1/2003; and

U.S. patent application Ser. No. 10/991,115, entitled "GEL PAD FOR USE WITH AN ULTRASONIC MONITOR", filed on even date herewith, the inventors of which are Thomas Ying-Ching Long, rong Jong Chang, attorney docket No. SALU-01003US0, all of which are incorporated herein by reference in their entirety.

Technical Field

The present invention relates to an ultrasonic monitor for measuring heart rate and pulse rate of a living subject.

Background

Measuring heart rate and pulse rate in living subjects has become a valuable tool in physical exercise and health monitoring. The pulse rate is measured by calculating the subject's arterial pulse rate. Heart rate is measured by sensing the electrical activity of the heart based on electrocardiograms (e.g., EKG and ECG). Individuals who wish to increase endurance or performance may wish to exercise while maintaining a target rate. Conversely, a subject with a history of heart disease or other heart related conditions should avoid exceeding a certain heart rate or pulse rate to reduce unnecessary stress on their heart.

The subject's heart rate is related to the pulse rate. Heart rate may be defined as the number of heart contractions over a particular time period, typically defined in beats per minute. Pulse is defined as the rhythmic dilation of a vessel due to the increase in the amount of blood forced through the vessel by the contraction of the heart. Since systole typically produces an amount of blood that can be measured as a pulse, the heart rate and pulse rate are ideally the same. However, during irregular or premature heart beats, the pulse rate may be different from the heart rate. In this case, the systole does not force enough blood through the blood vessel to be measurable as a pulse.

Most subjects requiring continuous heart rate readings select a monitor that requires a chest strap. While it continuously provides heart rate, the chest strap is cumbersome and often inconvenient to wear. In addition to chest strap solutions, portable patient monitors (e.g., vital signs monitors, fetal monitors) may perform measurement functions on a subject such as arrhythmia analysis, drug dose calculation, ECG waveform cascading, and the like. However, these monitors are typically quite large and are attached to the subject by uncomfortable leads.

The shallower depth of the radial artery at the wrist provides many advantages for achieving continuous pulse detection at the wrist. Existing sensors that monitor pressure pulses at the wrist are not effective. The pressure pulse is attenuated by the tissue between the artery and the sensor. Most of the high frequency signal components are lost due to this attenuation. In addition, muscle movements may generate a large amount of noise at the pressure sensor. The low frequency noise signal makes it very difficult to reliably identify the low frequency blood pressure pulses.

Ultrasonic monitors using sonar technology have been developed to overcome the noise signal problem. The ultrasonic monitor transmits ultrasonic energy as a pulse signal. When a power supply drives a transducer element (e.g., a piezoelectric crystal) to generate a pulse signal, an ultrasonic pulse signal is generated in all directions including the direction of an object to be measured (e.g., a blood vessel). The portion of the ultrasonic pulse signal that reaches the vessel is then reflected by the vessel. When a blood vessel undergoes motion (e.g., dilation due to blood flow from systole), the reflected pulse signal undergoes a frequency shift, also known as Doppler shift.

When an observer of the ultrasonic signal source or radar signal is in motion, a significant frequency shift will result. This is called doppler effect (doppleeffect). If R is the distance from the ultrasound monitor to the blood vessel, the total number of wavelengths λ contained in the bi-directional path between the ultrasound monitor and the target is 2R/λ. It is assumed that the distance R and the wavelength λ will be measured in the same units. Since one wavelength corresponds to an angular offset of 2 pi radians (angularexfusion), the total angular offset Φ created by the electromagnetic wave during its round trip through the vessel is 4 pi R/lambda radians. As the blood vessel undergoes motion, R and phase Φ change continuously. The change in Φ with respect to time is equal to the frequency. Which is the Doppler angular frequency W _d Given by:

wherein f is _d Is a Doppler frequency shift, and V _r Is the relative (or radial) velocity of the target relative to the ultrasonic monitor.

The amount of frequency shift is therefore related to the speed of the moving object reflecting the signal. Thus, for heart rate monitor applications, the flow rate or velocity of blood through a blood vessel is related to the amount of doppler shift of the reflected signal.

Piezoelectric crystals may be used as both the power generator and the signal detector. In this case, the ultrasonic energy is emitted in a pulsed mode. The reflected signal is then received by the same crystal after the output power is cut off. The time required to receive the reflected signal depends on the distance between the source and the object. Using a single crystal to measure heart rate requires high speed power switching due to the short distance between the source and the subject. In addition, muscle movement produces reflections that impair the signal-to-noise ratio in the system. The frequency range of the muscle motion noise is similar to the frequency offset detected from the vessel wall motion. Therefore, it is very difficult to measure the heart rate in this way. However, the advantages of this approach are low cost and low power consumption.

In some ultrasound signal systems, two piezoelectric elements are used to continuously measure the pulse. The two elements are positioned on a base plate (base plate) at an angle to the direction of the blood. In the continuous pulse rate measurement process, the frequency of doppler shift due to blood flow is higher than the frequency of shift due to myoelectric artifact (muscle artifact) or tissue motion. Thus, even if the muscle motion induced signal has a large amplitude, it can be removed by a high pass filter to preserve the higher frequency blood flow signal. The disadvantage of continuous mode over pulsed mode is higher cost and more power consumption.

Several wrist-mounted ultrasonic monitor devices are known in the art. However, the ultrasonic signal tends to diffract and attenuate at the interface of two media of different densities. Thus, air in the medium or between the monitor and the subject's skin makes the transmission of ultrasonic energy unreliable. Existing ultrasonic monitors require the application of water or aqueous gel between the transducer module and the living subject to eliminate any air gaps. Both water and aqueous gels are not a viable solution because they evaporate rapidly in the open air.

U.S. patent application Ser. No. 10/758,608, U.S. patent application No. 20040167409 to Lo et al disclose the use of thermoplastic and thermoset gels as transmission media for ultrasonic signals to overcome problems associated with water and aqueous gel solutions. In U.S. Pat. No. 6,716,169, muramatsu et al disclose a soft contact layer based on silicone gel (a thermoset gel) as the medium for ultrasonic signal transmission. These gels consist primarily of a large volume of non-evaporative (under ambient conditions) liquid diluent entrapped in a lightly cross-linked elastomer network. These crosslinked networks may be physical in nature (e.g., in thermoplastic gels) or they may be chemical in nature (e.g., thermoset gels).

Both gel types have disadvantages. First, the liquid diluent, although trapped in the elastomeric network, may diffuse into the user's skin after a prolonged period of contact. Since silicone gel uses silicone oil as a diluent, the diffusion of silicone gel is an important health concern. Therefore, there is a need to have a gel design that prevents the diffusion of oil into the living subject. Second, the soft gels of these known methods are difficult to handle. While softer gels allow better contact with the skin and result in better ultrasound transmission, soft gels are weaker and difficult to handle. It is highly desirable to have a gel design that is easy to handle but still maintains good ultrasound transmission. Third, the gels of the known prior art systems tend to accumulate dirt. Dirt on the gel surface results in poor contact with the skin and affects ultrasound transmission.

The efficiency of the transmitting transducer is an important feature of wrist-worn heart rate monitors and other small heart rate monitors. The transmission of ultrasonic signals by the transmitting transducer can be made more efficient by using reflectors. The transmitted signal generated from the target may be reflected by using reflectors at one or more sides of the transducer. Some heart rate monitors contain a foam with air holes under the piezoelectric crystal. As illustrated in fig. 1, the foam layer 120 may be placed within the ultrasonic module 110 below the

transducers

130 and 140. The foam pores partially inhibit ultrasonic energy penetration and provide a fairly effective reflection of ultrasonic signals. With such foam backings, some of the ultrasonic signals directed toward the foam are reflected toward the desired direction. A disadvantage of incorporating a foam layer is that it is installed manually during manufacture. Other prior systems increase efficiency by separating the two piezoelectric crystals with channels on the base plate. This reduces cross talk between the transducers to some extent but does not eliminate the loading or damping effect caused by the backplane.

There is a need for an improved heart rate monitor that provides continuous heart rate readings through a transmission medium that minimizes the air gap between the transducer and the living subject. The transmission medium should not dry out during monitoring, leave an uncomfortable wet film, or be prone to dirt accumulation. There is also a need for an ultrasonic monitor that is more power efficient but less expensive to produce.

Disclosure of Invention

The present invention relates generally to ultrasonic monitors. The ultrasonic monitor uses ultrasonic signals outside of a living subject to measure motion inside the body of the living subject. The movement may be a heart beat contraction, a movement of flowing blood or a blood vessel itself. Based on the information gathered from these movements, the electronics within the monitor can determine the blood flow rate, heart rate, or pulse rate of the living subject.

In one embodiment, the monitor is built on a circuit board (e.g., a Printed Circuit Board (PCB)). By being built on a PCB, the monitor system can be integrated to a very small footprint. This enables a very efficient system with much lower power requirements than existing systems. A pair of transducers is mounted directly to the PCB. This results in higher efficiency compared to previous implementations where the transducer was attached to some supporting structure (e.g., a glass backplane), thereby causing signal loading.

The PCB may be used to construct the ultrasonic signal reflecting layer. In one embodiment, a portion of the outer layer of the PCB is removed to form an air gap portion. The air gap functions in part to reflect ultrasonic signals. The transmitting transducer is mounted to the PCB over the air gap. When driven, the transmitting crystal generates an ultrasonic signal that travels toward the PCB in addition to the desired direction toward the target. The portion of the originally transmitted ultrasonic signal that travels toward the PCB is reflected off the PCB by the thin air gap and toward the intended target.

In some embodiments, multiple layers of gel pads are used to transmit ultrasonic signals between the ultrasonic monitor and the subject's skin. The gel pad includes a gel layer bonded to a membrane layer. A membrane layer may be applied to one or more surfaces of the gel layer and prevent the escape of diluents within the gel layer. This is advantageous when the gel contains elements that are not intended to be in contact with a living subject or other surface.

In another embodiment, the PCB may be completely encapsulated in plastic, a waterproof gel, or a combination of both. This serves to protect the ultrasonic monitor system from debris such as dirt, dust and water.

The ultrasonic monitor may include circuitry comprised of hardware, software, and/or a combination of both hardware and software. The circuitry demodulates the received ultrasonic signals as discussed with reference to figures 3-5. Software for the present invention is stored on one or more processor-readable storage media including hard drives, CD-ROMs, DVDs, optical disks, floppy disks, tape drives, RAM, ROM, or other suitable storage devices. In alternative embodiments, some or all of the software may be replaced by specialized hardware, including custom integrated circuits, gate arrays, FPGAs, PLDs, and special purpose computers.

Drawings

FIG. 1 illustrates a cross-section of a prior art ultrasonic monitor.

FIG. 2A illustrates one embodiment of an ultrasonic monitor physically connected to a display device.

FIG. 2B illustrates one embodiment of an ultrasonic monitor wirelessly connected to a display device.

FIG. 3 illustrates one embodiment of a block diagram of an ultrasonic monitor.

FIG. 4 illustrates one embodiment of a method of operating an ultrasonic monitor.

FIG. 5 illustrates one embodiment of a method of performing additional processing by an ultrasonic monitor.

FIG. 6 illustrates one embodiment of a perspective view of an ultrasonic monitor on a PCB with an air gap.

FIG. 7 illustrates one embodiment of a side view of an ultrasonic monitor on a PCB with an air gap.

FIG. 8A illustrates one embodiment of a perspective view of an ultrasonic monitor on a PCB having an air gap with a support member.

FIG. 8B illustrates one embodiment of a side view of an ultrasonic monitor on a PCB having an air gap with a support member.

FIG. 9A illustrates one embodiment of a perspective view of an ultrasonic monitor on a PCB having an air gap shared by two transducers.

FIG. 9B illustrates one embodiment of a side view of an ultrasonic monitor on a PCB with one air gap shared by two transducers.

Figure 9C illustrates one embodiment of a front view of an ultrasonic monitor on a PCB with one air gap shared by two transducers.

FIG. 10 illustrates one embodiment of a gel capsule (gel pouch) layer.

FIG. 11A illustrates one embodiment of a perspective view of a gel capsule.

FIG. 11B illustrates one embodiment of a side view of a gel capsule.

FIG. 12A illustrates one embodiment of a gel pad configuration.

FIG. 12B illustrates one embodiment of a gel pad configuration.

FIG. 12C illustrates one embodiment of a gel pad configuration.

FIG. 13A illustrates one embodiment of a perspective view of an ultrasonic monitor on a PCB with a mold.

FIG. 13B illustrates one embodiment of a side view of an ultrasonic monitor on a PCB with a mold.

Figure 14A illustrates one embodiment of a side view of an encapsulated PCB board.

Figure 14B illustrates one embodiment of a side view of an encapsulated PCB board.

Figure 14C illustrates one embodiment of a side view of an encapsulated PCB board.

FIG. 15A illustrates an embodiment of an ultrasonic monitor system with an encapsulated gel pad.

FIG. 15B illustrates an embodiment of an ultrasonic monitor system with a gel pad attached in situ.

Detailed Description

The present invention relates generally to ultrasonic monitors. The ultrasonic monitor uses ultrasonic signals to measure motion inside the body of a living subject. The movement may be a heart beat contraction, a movement of flowing blood or a blood vessel itself. Based on the information gathered from these movements, the electronics within the monitor can determine the blood flow rate, heart rate, or pulse rate of the living subject.

In one embodiment, an ultrasonic monitor measures blood flow through an artery of a human body. The frequency range of the ultrasound signal reflected due to vessel dilation (dilation due to blood movement through the vessel) is similar to the frequency range of noise due to myoelectrical artifacts and tissue movement. The frequency range of the ultrasonic signal reflected by the flowing blood itself is higher than the frequency range of noise associated with muscles and tissues. Thus, signals reflected by flowing blood are easier to process than those reflected due to dilation of the blood vessel itself to ascertain the value of the rate.

The terms ultrasonic and ultrasound are used interchangeably herein and refer to sound waves having a frequency between about 30KHz and about 30 MHz. As used herein, an ultrasonic transducer, transducer or transducer element is a device for introducing acoustic energy into a living subject and detecting reflected signals from the living subject. The ultrasonic transducer is responsive to the electrical pulses from the drive device and the ultrasonic pulses reflected by the subject.

The ultrasonic monitor includes an electronic portion and a transmission portion. The electronics portion includes the electrical components needed to transmit, receive and process ultrasonic signals as discussed with reference to fig. 3-5. Processing may include amplification, filtering, demodulation, digitization, squaring, and other functions (typically signal processing functions). The processing may be performed in whole or in part by digital circuitry. For example, the received ultrasonic signal may be digitized. The processing of the received signals described herein may then be performed by digital circuitry. The transmission portion includes a gel pad serving as a transmission medium between the monitor and the subject. The gel pad is positioned in direct contact with the living subject and the ultrasonic monitor.

In one embodiment, the monitor of the present invention is built on a Printed Circuit Board (PCB). By building the circuitry on the PCB, the monitor system is efficiently integrated into a very small footprint with greatly reduced power requirements. The transducer is mounted directly to the PCB.

The PCB may construct an ultrasonic signal reflecting layer. In one embodiment, a portion of the outer layer of the PCB is removed to form an air gap portion. The transducer elements are placed over the air gap portion. When driven, the transmitting crystal generates an ultrasonic signal that travels toward the PCB in addition to the desired direction toward the target. The portion of the originally transmitted ultrasonic signal that travels toward the PCB is reflected off the PCB by the thin air gap and toward the intended target.

In some embodiments, multiple layers of gel pads are used to transmit ultrasonic signals between the ultrasonic monitor and the subject's skin. The gel pad includes a gel layer bonded to a membrane layer. The membrane layer prevents the diluent in the gel layer from escaping. This is advantageous when the gel contains elements that are not intended to be in contact with a living subject or other surface.

In another embodiment, the PCB may be completely encapsulated in plastic, a water resistant gel, or a combination of both. This serves to protect the ultrasonic monitor system from debris such as dirt, dust and water. These advantages are discussed in more detail below.

The ultrasonic monitor may be implemented with a display. Figure 2A illustrates a wrist-worn ultrasound monitor system 200 in one embodiment. System 200 includes ultrasonic monitor module 210, strip 220, display device 230, and gel pad 240. Ultrasonic monitor module 210 detects blood flow through the radial artery at the subject's wrist. The heart rate data is then provided directly to the display module 230. In one embodiment, the connecting leads are molded as a strip 220 between the ultrasonic monitor module 210 and the display device 230.

The ultrasonic monitor may also be implemented with a remote display. Ultrasonic monitor system 250 of fig. 2B includes monitor module 260, first strip 270 attached to monitor module 260, remote display module 280, and second strip 290 attached to remote display module 280. The ultrasonic monitor module 260 detects blood flow through the radial artery in the wrist. The heart rate data is then provided to the remote display module 280. Monitor 260 may wirelessly transmit information to remote display 280 using a wireless transmitter. Remote display 260 includes a receiver for receiving transmissions from monitor 260. The remote display 280 may also be a monitor screen or other device. Ultrasonic monitor module 280 may be attached to another part of the body (e.g., the chest over the subject's heart) with an adhesive or gel pad.

The determination of which ultrasound signal frequency to use may depend on the particular subject being monitored. The wrist provides a convenient location for positioning the monitoring device. The relatively shallow depth of focus (focal depth) of the radial artery in the wrist requires the use of high frequency carrier signals.

The size of the transducer elements also affects the ultrasonic signal frequency. Smaller electromechanical resonators emit at higher frequencies. Transducer elements driven by high frequency signals tend to vibrate faster and consume more power than those operating at lower frequencies. This is mainly due to internal losses. The ultrasonic monitor amplifier and demodulation circuitry will also consume more power to process higher frequencies.

FIG. 3 illustrates a block diagram of one embodiment of an ultrasonic monitor system 300. Ultrasonic monitor system 300 includes a microcontroller 310, a transmit transducer element 320 coupled to microcontroller 310, a receive transducer element 330, a Radio Frequency (RF) amplifier 340 coupled to receive transducer 330, a mixer 350 coupled to RF amplifier 340 and microcontroller 310, an audio amplifier 360 coupled to mixer 350, and a Band Pass (BP) filter 370 coupled to audio amplifier 360 and microcontroller 310. The ultrasonic monitor system 300 may optionally include a local display 380 connected to the micro-controller 310, a wireless transmitter 390 connected to the micro-controller 310, a wireless receiver 392 receiving wireless signals from the wireless transmitter 390, and a remote display 394 connected to the receiver 392.

In one embodiment, the ultrasonic monitor may be implemented with a system similar to the system represented by block diagram 300, but having driver circuitry and high pass and low pass filters. In this case, the microcontroller drives the driver circuit with a carrier signal. The driver circuit drives the transmitting transducer to transmit an ultrasonic signal at a carrier frequency. The ultrasonic signal is reflected and received by the receiving transducer. The received signal contains a frequency offset that occurs from the signal transmitted by the transducer. The received ultrasonic signal is amplified by an RF amplifier circuit. The amplified ultrasonic signal is then processed by a mixer that demodulates the received signal and produces a signal having an audio range frequency. The resulting signal is then amplified by an audio amplifier circuit. The amplified audio signal is then filtered by a high pass filter circuit and a low pass filter circuit. The filtered signal is then received by the microcontroller. The microcontroller processes the filtered signal and provides an output signal to the wireless transmitter. The wireless transmitter transmits the signal to the receiver by a wireless method. The display then receives the signal from the receiver and displays information derived from the signal.

Method 400 of FIG. 4 illustrates the operation of one embodiment of an ultrasonic monitor, such as that represented by FIG. 3. At step 410, an ultrasound signal is transmitted. Referring to system 300, microcontroller 310 is provided with a carrier signal f _C To drive the transmitting transducer element 320. Thus, the transmitting transducer generates an ultrasonic signal. In one embodiment, the carrier signal may be in the range of 30KHz to 30 MHz. In another embodiment, the carrier signal may be in the range of 1MHz to 10 MHz. In yet another embodiment, the carrier signal is about 5MHz.

At step 420, the reflected ultrasonic signal is received. The reflected ultrasound signal is generated by the vascular reflection step 410 of the ultrasound signal. The radial artery reflects the signal when the ultrasonic monitor is worn on the wrist. The received ultrasonic signal will contain an ultrasonic carrier frequency that has undergone a doppler shift from the signal transmitted by the transmitting transducer 320. The received signal is then amplified at step 430. In one embodiment, amplifier 340 of system 300 is implemented as a radio frequency amplifier. The received ultrasonic signal is amplified by a factor that allows it to be processed for demodulation. Once the ultrasonic signal is amplified at step 430, it is processed by mixer 350 at step 440. Frequency mixer using carrier signal f _C To demodulate the reflected ultrasonic signal to extract a doppler signal. Thus, the mixer 350 is fed by the carrier signal f _C And the reflected ultrasonic signal. The output signal provided by mixer 350 is then amplified by amplifier 360 at step 450. Since the output of the mixer will have frequency components in the audio range, amplifier 360 is an audio amplifier designed to amplify the demodulated audio range doppler frequency.

After the demodulated signal has been amplified, the amplified signal is filtered at step 460. In one embodiment, the filter of step 460 is a band pass filter. The band pass filter may be configured to remove aliasing effects, noise, and other unwanted frequency factors. In another embodiment, a band pass filter may be implemented with a high pass filter and a low pass filter. After filtering the signal at step 460, the signal undergoes additional processing at step 470.

The additional processing of step 470 may include several steps depending on the ultrasonic monitor system. The processing may be performed by a microcontroller or other circuitry. Although the method is varied, a typical example of additional processing is illustrated in method 500 of FIG. 5. The filtered signal from step 460 of method 400 is processed by an analog-to-digital converter at step 510. In one embodiment, the digitizing is performed if the digitizing has not been performed previously. Next, at step 520, the absolute value of the digitized signal is determined. Alternatively, the square of the signal may be determined at step 520. Next, the signal obtained from step 520 is filtered by a low pass filter in step 530. The low pass filter removes noise and other unwanted frequency components of the signal. Method 500 is an example of additional processing performed by an ultrasound system. It should be appreciated that the processing of the signals may vary from system to system, and embodiments of the ultrasonic monitor are not intended to be limited solely to the scope of the examples discussed. The heart rate is then acquired at step 540. After the processing of steps 510-530, the resulting signal is a pulsed signal retrieved from the receiving transducer. The signal appears as a series of pulses, where each pulse has an area determined by the path of its amplitude to and from the peak amplitude. The resulting heart rate or pulse rate is obtained from the frequency of the pulses (e.g., 160 pulses per minute corresponds to 160 heart beats per minute). The flow rate is determined by integrating the area under the pulse waveform.

The microcontroller of the ultrasonic monitor can be implemented as one or more of several common microcontroller integrated circuits, including Samsung KS57C 3316 series, samsung S3C7335, intel 8051 series, and Texas Instruments MSP430 series microcontrollers. The mixer of the ultrasonic monitor may be implemented as one or more of several commonly used mixer ICs or frequency modulation ICs. A non-exhaustive list of possible mixer ICs includes the NJM2295, NJM2292 and NJM2537 mixers of a NJC, the TK8336IM mixer of Toko, and the MC3371 mixer of Motorola.

The transducers used in the present invention adhere to some common design criteria. The transducer of the ultrasonic monitor may be a piezoelectric transducer. The length of each transducer is typically at least one centimeter long. The transducer length is also typically equal to or greater than five times its width. The frequency at which the transducer operates is typically related to the thickness of the transducer. Several types of transducers may be used in the present invention. One example is the K-350, modified lead zirconate titanate transducer supplied by Keramos Division, piezo Technologies. Equivalent materials for this type of transducer include PZT-5A or NAVY-II equivalents.

Ultrasonic monitor on circuit board

One embodiment of an ultrasonic monitor system is built on a Printed Circuit Board (PCB). The monitor may be built on a PCB using PCB techniques such as Surface Mount Technology (SMT) and Chip On Board (COB). Building the circuitry on a PCB integrates the monitor system to a very small footprint. This enables a more efficient system, lower power requirements, consistent product performance, and reduced production costs.

Building the monitor system on a PCB allows for easy construction of the air gap portion. To form the air gap portion, one or more sections of the outer layer of the PCB are removed. The transducer is then placed over the air gap portion. This forms an air gap portion with one or more air gaps below the transducer element. The air gap portion reflects the ultrasonic signal off the PCB and toward the desired direction. The air gap is much more efficient and easier to construct than the foam layer of prior systems. In addition, the transducer elements are mechanically isolated due to the air gap, thereby reducing any damping or loading effect on the transducer due to contact by any other material. The air gap also serves to significantly reduce, if not eliminate, crosstalk noise between the transducers. In some embodiments, additional layers may be removed from the PCB to create air gap portions of greater thickness. In this case, additional etching, drilling, or other methods may be used to control the depth of the air gaps. In some embodiments, an air gap may be created that penetrates the entire circuit board. This method can simply create an air gap that effectively reflects the ultrasonic signal.

The ultrasonic monitor transmits ultrasonic signals more efficiently than prior monitors. The ultrasonic monitor transducer is mounted directly to the PCB using conductive epoxy or solder paste. The transducers of previous systems are typically glued completely to the support structure (e.g., glass base plate). Attaching the entire surface of the transducer to the support structure creates a mechanical load that dampens the vibration of the transducer. The damping reduces efficiency and draws power from the ultrasonic signal. The transducer of the present invention can generate the same ultrasonic signal as that of the previous system using less power due to the minimized load.

The PCB may include several layers, such as a power layer, a ground layer, and an insulating layer. The insulating layer may electrically isolate the transducer from the monitor system. In some four-layer PCBs, there are four copper layers and three insulating layers. Two copper layers are the outer layers and two are the inner layers. In one embodiment, one of the inner copper layers immediately adjacent to the transducer may be used as a ground plane or layer in order to electrically isolate the two transducers from interfering with the rest of the circuitry on the PCB. This inner copper layer ground plane will shield RF interference generated or received by the transducer. This prevents the circuitry from causing interference with the transducer signal transmission. In one embodiment, one surface of the PCB may be used to build the monitor system circuitry and the opposite surface may be used to mount the transducer. In another embodiment, the transducer may not be built on the same PCB as the monitor system circuitry.

FIG. 6 illustrates a top view of one embodiment of a monitor 600 built on a PCB. The monitor 600 includes an outer layer 610, a first transducer 622 and a second transducer 624 mounted to the outer layer 610,

air gaps

626 and 627 residing below the

transducers

622 and 624, respectively,

dedicated copper pads

630 and 635, and connecting leads 640 and 645 connected between the

dedicated copper pads

630 and 635 and the

transducer elements

622 and 624, respectively. In one embodiment, the outer layer 610 is composed of a conductive material such as copper plated with tin or gold.

Fig. 7 illustrates a side view of the monitor 750 implemented on a PCB and further illustrates circuitry 760 attached to an opposite surface of the PCB. The circuit 760 includes surface mount ICs and electrical components (e.g., resistors and capacitors) that can implement the electrical system of the ultrasonic monitor.

Most, if not all, construction of the PCB is automated. The application of solder paste, placement of transducer elements, and wire bonding can all be automated by existing PCBA production techniques. This significantly reduces the manufacturing cost. For typical electronic components in surface mount packages, such as resistors, capacitors, and integrated circuits, a stencil (solder) is used to first apply solder paste to one side of the PCB. The components are then placed by an automatic pick and place machine. The PCB is then subjected to an Infrared (IR) furnace, which melts the solder paste and forms electrical connections between the components and the underlying circuitry pre-etched on the PCB. The same steps can be applied to mount the transducer elements on opposite sides of the PCB. This greatly reduces the cost of production and enhances product performance consistency.

The

air gap portions

626 and 627 of fig. 6 and 7 are constructed by removing a portion of the outer layer. A chemical etch may be performed to remove a portion of the outer layer of the PCB. Therefore, the depth of the air gap portion is the thickness of the layer removed. The area of the outer layer 610 that is etched away is proportional to the surface area of the

transducers

622 and 624. The

air gap portions

626 and 627 are configured such that the

transducer elements

622 and 624 slightly overlap the air gap portions. This overlapping of the transducers allows the ends of the transducers to be mounted to the outer layer of the PCB.

The air gap portion of the present invention can be constructed in several ways. In the embodiment illustrated in fig. 6 and 7, the air gap portion is a single undivided area beneath each transducer. The air gap extends about as long as the width of the transducer and slightly shorter than the length of the transducer. Fig. 8A is a top view of an embodiment of a monitor 800 built on a PCB. Monitor 800 includes a PCB outer layer 810,

transducers

822 and 824 connected to the outer layer,

air gaps

826 and 827 under transducer 822 and separated by support member 830,

air gaps

828 and 829 under transducer 824 and separated by support member 831, copper contact pads 840, and connecting leads 845 connecting copper pads 840 to

transducers

822 and 824. Fig. 8B is a side view of monitor 800 built on a PCB and further illustrates circuitry 860 attached to the opposite surface of the PCB. The air gap portion of fig. 8A and 8B includes two air gaps. The air gap portion extends about as long as the width of the transducer and slightly shorter than the length of the transducer. However, the air gap portion of each transducer contains a support member. Thus, the air gap portion of transducer 822 includes air gap 826, air gap 827, and support member 830, and the air gap portion of transducer 824 includes air gap 828, air gap 829, and support member 831.

The support member is constructed by leaving a portion of the outer layer of the PCB on which the transducer will reside. In the embodiment of fig. 8A and 8B, the

support members

830 and 831 are thin strips that extend across the width of the air gap portion and are located approximately at the middle of the transducer length. In different embodiments, the support members may be constructed in different shapes and positions within the air gap portion of the PCB. For example, the support members may be implemented as strips that extend less than the entire width of the air gap portion, strips along the length of the air gap portion, or as multiple small areas within the air gap portion. When implemented as one or more regions, the support members may be isolated from the remainder of the outer layer or in contact with a portion of the outer layer. The support member may support the transducer in case the transducer receives pressure from an external force.

Fig. 9A-C depict an embodiment of a monitor 900 built on a PCB. Fig. 9A provides a top view of monitor 900. Monitor 900 includes a first layer 910, mounting

layers

940 and 942 attached to the first layer,

transducers

920 and 922 mounted to mounting

layers

940 and 942, respectively, an air gap 945 located below

transducers

920 and 922,

air gap channels

946 and 948 located between mounting

layers

940 and 942, and a copper pad 951. The mounting

layers

940 and 942 have a u-shape. The mounting layer may be constructed by removing a portion of the PCB layer to form a u-shaped layer or by attaching a u-shaped member to a layer of the PCB. In some embodiments, one or more mounting layers having different positions and shapes than those illustrated in FIGS. 9A-C may be implemented to support each transducer and provide an air gap beneath each transducer. Fig. 9B is a cross-sectional side view of monitor 900 from the point of view indicated by the arrow in fig. 9A. FIG. 9B illustrates the monitor being implemented on a PCB, with transducer 920 mounted to mounting layer 940, mounting layer 940 attached to first layer 910, air gap 930 beneath transducer 920, and circuitry 960 attached to the opposite surface of the PCB. Fig. 9C is a front view illustrating monitor 900. In the monitors of fig. 9A, 9B and 9C, the outer layer is removed to form an undivided air gap beneath the

transducers

920 and 922. The removed portion extends around the transducer to reveal portions of underlying layer 910 not covered by the transducer elements.

As illustrated in the PCBs of fig. 7A-B, 8A-B and 9A-C, the transducers are mounted at the outer layers of the PCB where the transducer length slightly overlaps the air gap portion. In some embodiments, the air gap portion may be formed such that the transducer is mounted to the PCB where the transducer width slightly overlaps the air gap. In one embodiment, the width and length of the air gap portion will not be made larger than the width and length of the transducer elements. This prevents any silicone-based epoxy or molten thermoplastic gel that may be applied to the transducer from entering the air gap portion. If the epoxy or gel does penetrate the air gap, the acoustic impedance of the gel and the exposed fiberglass material comprising the PCB is sufficiently different that the ultrasonic energy will still be effectively reflected toward the desired direction. Since the air gap is relatively thin, the energy loss (if any) will be negligible.

Gel pad for ultrasonic frequency transmission

The gel pad is used to transmit ultrasonic frequency signals between the ultrasonic monitor and the subject. The gel pad is in contact with the skin of the subject and the transducer or a surface in direct or indirect contact with the transducer (e.g., an RTV layer). Gels with high oil content are generally transparent to ultrasound. Thus, energy losses during transmission are significantly minimized. This enables the ultrasonic monitor to effectively measure the blood flow rate and cardiac output accurately.

In one embodiment, the gel pad may be constructed as a gel capsule. FIG. 10 illustrates one embodiment of a gel capsule. Gel pouch 1000 includes a gel layer 1010,

primer layers

1020 and 1030,

membrane layers

1040 and 1050, and

adhesive layers

1060 and 1070. The gel layer 1010 is the primary transmission medium for the gel capsule. A primer layer may be applied to the surface of the gel layer. In embodiments where the gel layer is generally shaped to have top and bottom surfaces, the primer layer may be applied as upper primer layer 1020 and/or lower primer layer 1030. The membrane layer is attached to the gel layer via the primer layer. The membrane layer is used to assist in handling the softer gel and to prevent the diluent from coming into contact with the subject's skin. An upper membrane layer 1040 is attached to upper primer layer 1020 and a lower membrane layer 1050 is attached to lower primer layer 1030. A membrane layer may be applied to one or more surfaces of the gel layer. An adhesive layer may then be applied to the outer surface of the separator layer. The adhesive is used to attach the gel capsule to the skin of the subject, the transducer, or an RTV element in contact with the transducer. The adhesive may also eliminate any air pockets that may exist between the gel pouch and other surfaces. An upper adhesive layer 1060 may be applied to the upper membrane layer 1040 and a lower adhesive layer 1070 may be applied to the lower membrane layer 1050.

FIG. 11A illustrates a top view of one embodiment of a gel pad 1180. Gel pad 1180 includes gel pouch 1182, first cover 1184, and second cover 1186. FIG. 11B illustrates a side view of gel pad 1180. Gel pouch 1182 generally maintains a flat, disk-like shape. The cover is applied to the gel capsule during manufacture and protects it before it is used. The cover may be constructed of waxed paper or some other type of material. For an ultrasonic monitor, the gel pouch is used as a disposable gel pad. Just prior to use, the cover is removed from the gel pouch. A gel capsule is then applied to the area between the ultrasound monitor and the subject's skin. In one embodiment where the monitor is worn on the wrist, the gel pouch is applied between the wrist worn monitor and the subject's wrist. One embodiment of the monitor provides a recess in an outer surface of the monitor applied to the subject. The gel capsule may be applied to a recessed area on the monitor to help keep it in place. The gel pad may be adhered to the monitor and subject when the gel pad includes a pressure sensitive adhesive and is compressed between the monitor and subject. The gel pad may be compressed when: the monitor is strapped, secured, or otherwise applied to the subject with straps, held in place without straps for a period of time, or in some other manner.

The gel pad shape and thickness can be designed to allow the ultrasonic monitor to operate at different deflection angles. The gel pad orientation 1200 of fig. 12A illustrates a monitor module 1205 attached to a gel pad 1210 having a rectangular cross-section. Gel pad orientation 1220 of fig. 12B illustrates monitor module 1225 attached to gel pad 1230 having a triangular cross-section. The gel pad orientation 1240 of fig. 12C illustrates a monitor module 1245 attached to a gel pad 1240 having a trapezoidal cross-section. The size of these gel pad shapes is based on the desired deflection angle and the depth of the moving object to be detected.

Several types of materials can be used to construct the gel pad of the present invention. The gel layer of the gel pad (gel 1010 of fig. 10) may be constructed from a thermoplastic gel, a thermoset gel, a hydrogel, or other similar materials. Thermoplastic gels are typically made from thermoplastic elastomers with a large proportion of inter-dispersed diluent. The thermoplastic elastomer comprises block copolymers, for example, styrene-butadiene-styrene, styrene-isoprene-styrene, styrene/ethylene-co-butylene/styrene, and styrene/ethylene-co-propylene/styrene. The styrene end blocks form glassy domains at room temperature. The glassy domains act as physical crosslinks that provide the elastomeric properties of the polymer. During heating above the glass transition temperature of styrene (i.e., about 100 ℃), the glassy domains melt and the polymer returns to a liquid state. During cooling, the glassy domains reshape again. Thus, the process is reversible. Other block copolymers containing crystalline polyethylene end blocks (e.g., ethylene- (ethylene-co-butylene) -ethylene copolymers) can also be used to prepare thermoplastic gels.

Thermoset gels (e.g., polyurethane or silicone gels) are typically made of chemically bonded three-dimensional elastomeric networks that retain a large amount of low volatility liquid or diluent. The elastomeric network is permanent and cannot be restored to a liquid state by heating. It is necessary to use a certain amount of diluent in order to ensure good adaptation of the gel to the skin and low attenuation of the ultrasound transmission, while still maintaining the load bearing properties. The gel may be used at temperatures in the range of-30 ℃ to +70 ℃, in which the gel retains its shape and load-bearing elastic properties.

Thermoset gels and thermoplastic gels invariably contain a large percentage of diluent entrapped in the elastomeric network. When properly formulated, these gels are stable and can resist stress or temperature cycling. Stability is controlled by thermodynamic factors such as the crosslink density of the elastomeric network and the compatibility of the diluent with the elastomeric network. However, even a thermodynamically stable gel, when in contact with the skin, the diluent in the gel may still diffuse out and into the living subject. This is due to the fact that: the dilution on the skin has a concentration gradient; the natural tendency of the diluent is to migrate out of the gel (where the diluent concentration is higher) and into the skin (where the initial concentration of the diluent is zero). Thus, the diffusion is kinetically controlled by Fick's Law. The diffusion of diluents (especially silicone oils) can have a detrimental effect on the organism. In one embodiment, the diluent is prevented from diffusing by bonding or laminating a compliant barrier membrane to the gel layer.

Hydrogels can be composed of water soluble polymers such as polyacrylic acid, polyacrylamide, poly (acrylic acid-co-acrylonitrile), poly (acrylamide-co-acrylonitrile), and the like. It is dissolved in a large amount of water of approximately 50% to 98% by weight of the total mixture. The mixture is optionally thickened by ions such as sodium, zinc, calcium, etc., which are provided by the addition of corresponding metal salts. When used with a membrane, the membrane may effectively seal the mixture from water evaporation or migration.

The membrane layer may be made of polyurethane, silicone, poly (vinyl chloride), natural or synthetic rubber, polyester, polyamide, or a film of polyolefin including low density polyethylene, plastomers, metallocene olefin copolymers or other similar materials. Virtually any thin polymer film that is flexible and suitable is within the scope of the present invention. One skilled in the art can determine the appropriate separator material depending on the gel material selected. The membrane may be laminated to the gel pad using an adhesive. The membrane may also be formed by spraying or coating a film-forming liquid, such as a polyurethane elastomer solution or latex, onto the surface of the gel layer. Upon drying the liquid, a thin membrane is formed, which can achieve the same result as the lamination process. Depending on the type of diluent in the gel layer, the membrane is chosen to provide the best barrier effect. The membrane is preferably as thin and flexible as possible so that it conforms better to the skin and minimizes the possibility of air entrapment. The membrane also allows for easier gel pad handling, reduced dirt accumulation, and easier cleaning.

Several types of adhesives and primers (primer) can be used to create the gel capsules of fig. 10 and 11A-B. For example, 3M may be used ^TM Provided Automix ^TM Polyolefin adhesion promoters 05907 and Loctite from Loctite ^TM 770 the polyolefin primer acts as a primer between the gel layer and the membrane layer. AROSET available from Ashland specialty chemical Company may be used ^TM 3250 the pressure sensitive adhesive acts as an adhesive between the membrane layer and the skin of the subject. Dow Corning can be used ^TM DOWCORNING7657 adhesive for use with SYL-OFF4000 catalyst was provided as an adhesive between the barrier layer and the RTV member.

Depending on the base material of the gel, the pressure sensitive adhesive applied to the outer surface of the membrane layer may be based on rubber, silicone or acrylic polymers. For example, if a thermoplastic gel is used, a rubber-based pressure sensitive adhesive will provide better adhesion. It is also preferred that the pressure sensitive adhesive is medical grade without causing skin sensitization. It is also desirable that the membrane itself not cause skin sensitization if the membrane is in direct contact with the skin. Some membrane materials made from natural rubber latex are known to cause allergic reactions to some people's skin.

In another embodiment, the gel pad may be comprised of a single layer of thermoplastic gel material. This is particularly convenient when using a biocompatible fluid such as medical mineral oil as the diluent in the gel. Such oils, if they migrate into the skin, do not have a deleterious effect on the living tissue. For example, baby oil (a medical mineral oil) may be used as the diluent. In this case, the thermoplastic gel material is sufficiently conformable to the surface of the subject such that no adhesive is required between the gel pad and the skin of the subject. In particular, when a slight amount of pressure is applied (e.g., by an ultrasonic monitor worn on the wrist with a wrist strap), any existing air pockets are substantially eliminated. A minimum adhesion force is required to hold the single layer thermoplastic gel pad in place while in contact with the ultrasonic monitor and the subject's skin. This is advantageous because it is simple and inexpensive to construct, and allows the use of large amounts of adhesive to hold the gel pad in contact with the RTV. In one embodiment, the thickness of the gel may be between about 1 and 10 millimeters. In some embodiments, the thickness of the gel may be between 1 and 5 millimeters.

The gel pad may be attached to the ultrasonic monitor in several ways. In one embodiment, the thermoplastic gel may be heated to a molten state and overmolded (over-mold) onto the plastic housing of the transducer. Although the thermoplastic gel will adhere to the transducer, an adhesive may be used to ensure a durable bond. Examples of such binders include Versaflex6000 supplied by GLS Corporation and Monprene supplied by Teknor Apex Corporation. In one embodiment, the adhesive may be overmolded by injection molding prior to overmolding the gel. An adhesive suitable for overmolding comprises EC6000 supplied by eclectic PRODUCTS, inc. The membrane layer may then be laminated over the gel layer to prevent the diffusion of the diluent.

In another embodiment, a mold is used to form a portion of the transmission medium. In this case, a mold surrounding the transducer and a portion of the outer surface of the PCB is mounted to the PCB. Next, a Room Temperature Vulcanizing (RTV) silicone rubber layer adhesive was placed in the mold. Although the RTV layer will adhere to the exposed PCB surface within the mold, an adhesive may be used to further secure the RTV to the PCB. RTVs provide excellent ultrasonic signal transmission and are slightly stronger than thermoplastic gel pads. The robustness of the RTV layer prevents damage to the transducer elements due to contact with gel pads and other objects.

An embodiment of a PCB system incorporating a molded RTV layer is shown in FIGS. 13A and 13B. The monitor of the system 1300 of FIG. 13A includes an outer layer 1310 of a PCB, transducers 1320 and 1330 mounted to the outer layer, an RTV mold 1340, copper contacts 1342, connecting leads 1344 connecting the copper contacts 1342 to the transducers 1320 and 1340, air gap portions 1322 and 1324 below the transducer 1320, and air gap portions 1326 and 1328 below the transducer 1330. FIG. 13B illustrates a side view of the PCB system, and further illustrates circuitry for implementing the monitor mounted to the opposing surface of the transducer. The RTV mold is configured such that it encompasses the transducer, the air gap portion, and a portion of the outer layer of the PCB. The connecting leads 1344 may be located above or below the mold. The mold may be constructed as a solder mold and attached to the PCB using a suitable adhesive as discussed above. During production, the RTV material is placed in an RTV mold. The gel pad may then be attached to the RTV using a suitable adhesive.

In one embodiment, the gel layer portion of the gel pad can be molded over the RTV material. The membrane layer and/or the polyurethane portion of the gel pad may then be applied to the outer surface of the gel layer. The separator layer may be applied with or without an adhesive. In this embodiment, a membrane layer is not applied to the surface of the gel layer that is in contact with the RTV layer (i.e., no membrane is used between the RTV material and the gel layer in this embodiment). The outer surface of the membrane layer may then be placed in contact with the skin of the subject. An adhesive may be applied to the outer surface of the membrane layer that is in contact with the skin of the subject, if desired.

The RTV material may be chosen such that it acts as a mechanical spacer between the transducer and external forces. The RTV material absorbs external forces (e.g., contact with the subject's skin or skin pressure from the subject) and prevents it from affecting the resonant frequency of the transducer. RTVs may be constructed from several types of materials, including all materials made from DOWCORNING ^TM Silastic is provided ^TM ERTV silicone rubber and DOWCORNING3110, 3112 and 3120RTV rubber. CORNING can be used ^TM 1301 the primer and other similar primers attach the RTV material to the PCB.

Encapsulated ultrasonic monitor

In one embodiment of the invention, the ultrasonic monitor may be encapsulated to make it waterproof. The ultrasonic monitor may be sealed using ABS plastic material, gel material, or both. For example, the electronics side may be sealed in an ABS plastic material, while the transducer side is sealed by a softer gel material (e.g., a high oil content thermoplastic material). In another embodiment, both the transducer side and the electronics side may be sealed using ABS plastic material.

The sealed assembly may be formed with a recess above the transducer or RTV portion of the ultrasonic monitor. A disposable gel pad may be placed in situ at the recessed area to improve ultrasonic signal transmission and maintain the position of the gel pad. The gel pouch illustrated and discussed with reference to fig. 11A-B may be used in this embodiment. In some embodiments, the resulting assembly may be further molded or somehow mechanically coupled to a polyurethane-based watch band. Both final assemblies will be waterproof and maintain good ultrasonic transmission characteristics for the subject.

FIG. 14A illustrates an embodiment of a sealed ultrasonic monitor 1400. Monitor 1400 includes PCB 1410, circuitry 1412, plastic housing 1414, gel or epoxy layer 1420, transducers 1422 and 1424, and gel pad 1425.PCB 1410, circuitry 1412 are molded and sealed in a plastic (e.g., ABS plastic) housing 1410. A gel or epoxy layer 1420 is molded or cast over the transducer and seals the plastic housing.

FIG. 14B illustrates an embodiment of a sealed ultrasonic monitor 1430. Monitor 1430 includes PCB 1440, circuitry 1442, plastic housing 1444, adhesive layer 1450, gel or epoxy layer 1452, transducers 1454 and 1456, and gel pad 1458. Monitor 1430 is similar to monitor 1400 except that adhesive layer 1450 is applied over the transducer and PCB.

Figure 14C illustrates an embodiment of a sealed ultrasonic monitor 1460. Monitor 1460 includes a PCB 1470, a circuit 1472, a plastic housing 1474, a gel or epoxy layer 1480, transducers 1482 and 1484, and a gel pad 1490. Monitor 1460 is similar to monitor 1400 except that a plastic housing 1474 surrounds the entire monitor.

The encapsulated ultrasonic monitor can be used with a permanently attached gel pouch or a disposable gel pouch that can be attached in the field. FIG. 15A illustrates an embodiment of a wrist-worn ultrasonic monitor 1500 enclosed in a housing. Monitor 1500 includes an ultrasonic monitor module 1510, a gel pad 1515 attached to monitor module 1510, a display device 1530, and a strap 1520 attached to the display device and monitor module. The gel capsule 1515 is attached to the monitor module during production. In one embodiment, the gel pad may be attached to the monitor module 1510 by a molding process. Figure 15B illustrates one embodiment of a wrist worn ultrasonic monitor 1580 enclosed in a housing. Monitor 1580 includes an ultrasonic monitor module 1560, a disposable gel pad 1565 attached to monitor module 1560, a display device 1580, and a strap 1570 attached to the display device and monitor module. The disposable gel pouch 1565 may be attached to the monitor module just prior to use of the monitor.

Ultrasonic monitor modules

1510 and 1560 have slightly different shapes. This is merely to provide an example. The shapes of the ultrasonic monitor modules of fig. 15A and 15B are interchangeable and are not intended to limit the scope of the invention.

The foregoing detailed description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.

Claims

1. An ultrasonic monitor, comprising:

a circuit board; and

one or more ultrasonic transducers mounted to the circuit board such that there is one or more air gaps between the circuit board and the one or more transducers.

2. The ultrasonic monitor of claim 1, wherein the one or more air gaps include a first air gap positioned below a transmitting transducer and a second air gap positioned below a receiving transducer.

3. The ultrasonic monitor of claim 2, wherein the first air gap has an area about the same size as an area of the transmitting transducer element and the second air gap has an area about the same size as an area of the receiving transducer element.

4. The ultrasonic monitor of claim 1, wherein the one or more air gaps are formed by removing a portion of the circuit board.

5. The ultrasonic monitor of claim 1, wherein the one or more air gaps are undivided air gaps below a transmitting transducer and a receiving transducer.

6. The ultrasonic monitor of claim 1, wherein the air gap portion includes a support member below each of the transmit transducer element and the receive transducer element.

7. The ultrasonic monitor of claim 1, wherein the one or more air gaps include two air gaps separated by a support member, at least one transducer mounted over the support member.

8. An ultrasonic monitor, comprising:

a circuit board having an outer layer;

a transmitting transducer mounted to the circuit board;

a receive transducer mounted to the circuit board, the outer layer including one or more air gaps below the transmit transducer elements and the receive transducer elements; and

circuitry configured to process the received ultrasonic signal.

9. The ultrasonic monitor of claim 8, wherein the one or more air gaps are formed by removing a portion of the outer layer.

10. The ultrasonic monitor of claim 8, wherein the transmitting transducer and the receiving transducer have lengths slightly longer than the air gap portion.

11. The ultrasonic monitor of claim 8, wherein the one or more air gaps are undivided portions below the transmit transducer and the receive transducer.

12. The ultrasonic monitor of claim 8, wherein the one or more air gaps include a support member below each of the transmitting transducer and the receiving transducer.

13. The ultrasonic monitor of claim 12, wherein the support member is comprised of a strip of an outer layer of the circuit board.

14. The ultrasonic monitor of claim 8, further comprising:

a housing component containing the transmitting transducer, the receiving transducer, and the circuitry.

15. The ultrasonic monitor of claim 14, further comprising:

a strap member connected to the housing member.

16. A method for constructing an ultrasonic monitor, comprising:

accessing a circuit board;

removing at least a portion of a layer of the circuit board to form one or more air gaps; and

one or more transducers are mounted to the circuit board such that the one or more air gaps are between the one or more transducers and the circuit board.

17. The method of claim 16, wherein the step of removing at least a portion of the outer layer is performed by chemical etching.

18. The method of claim 16, wherein the step of removing at least a portion of the outer layer comprises creating an aperture in the circuit board.

19. The method of claim 16, wherein removing a portion of the circuit board comprises:

removing a first portion of the circuit board to form a first air gap; and

removing a second portion of the circuit board to form a second air gap, the first air gap and the second air gap being isolated from each other by a portion of the circuit board, the circuit board configured to receive a transmitting transducer over the first air gap and a receiving transducer over the second air gap.

20. The method of claim 19, wherein removing the first portion comprises:

removing a region of the outer layer that is about the same size as the transmitting transducer except for a support member positioned to support a portion of the transducer.

21. The method of claim 20, further comprising:

mounting a transmit transducer, a receive transducer, and a circuit to the circuit board, the transmit transducer and receive transducer being mounted directly to the circuit board over the air gap portion.

22. A method for monitoring heart rate, comprising:

transmitting an ultrasonic signal from a transmitting transducer mounted on a circuit board, the ultrasonic signal being transmitted in a first direction toward a target located away from the circuit board and in a second direction toward the circuit board;

reflecting the signal transmitted toward the circuit board toward the target through an air gap positioned below the transmitting transducer; and

the reflected ultrasonic signal is received by a receiving transducer.

23. The method of claim 22, wherein the air gap is formed by removing a portion of the circuit board under one of the transducers.

24. The method of claim 22, wherein the air gap portion is positioned below both the transmitting transducer and the receiving transducer.

25. The method of claim 22, wherein the air gap is an aperture through the circuit board.

26. The method of claim 22, wherein reflecting comprises:

reflecting the signal with a first air gap and a second air gap, the first air gap and the second air gap being isolated from each other by a portion of the circuit board.

27. The method of claim 22, wherein the first air gap portion includes a support member composed of a portion of an outer layer of the circuit board and positioned below the transmitting transducer.